Theoretical design of the molecular structure of bent-core mesogens with large second-order nonlinear optical properties.

The first hyperpolarizability of two series of molecules with bent-shaped structures has been calculated at the ab initio level. The two series consist of carboxyl derivatives for which some molecules are known to exhibit banana phases and of their sulfinate homologues that have not been synthesized yet. The final purpose is to reveal the relevance or not in synthesizing these latter molecules. The strategy is based on reporting the effect of the positions of donor and acceptor groups on the central benzene ring on the structural parameters and on the first hyperpolarizabilities. It is shown that in the sulfinate series the larger first hyperpolarizabilities are incompatible with efficient geometrical character while for the carboxyl series, the opening angle between the molecular arms is typical of banana-shaped molecules but the first hyperpolarizability is only slightly enhanced. Calculations thus reveal that the sulfinate series does not need to be synthesized, whereas they show that our approach can be naturally applied to the development of new bent-shaped molecules for nonlinear optical applications.